An image sensor is a device including several million photoelectric conversion devices for converting light into an electric signal, depending upon the intensity of the light received by the device. Image sensors can be used in digital input devices, which enable digitalizing recorded images. There is a rapidly increasing demand for such devices for use in various applications such as security devices and digital portals.
Image sensors include a pixel array in which a plurality of pixels is arranged in a matrix form, and each pixel includes a photo-sensing device and a transmitting and signal output device. Image sensors are broadly categorized as charge coupled device (CCD) image sensors or complementary metal oxide semiconductor (CMOS) image sensors, depending upon the transmitting and signal output device. The CMOS image sensor concentrates the outside light through a micro-lens, the concentrated light is transmitted to a photo-sensing device such as a photodiode and the signal is output.
CMOS image sensors can be further modified to increase resolution, and recently research on decreasing pixel size to 1 μm or less has been undertaken. As pixel size decreases to 1 μm or less, however, consideration must be given to the geometric optical aspect and wave optical aspect in relation to the micro-lens since the size of the unit pixel can be up to 1.5 times the visible ray wavelength. Further, as the unit pixel becomes smaller, the diameter of the micro-lens becomes smaller. Thereby, a crosstalk phenomenon between adjacent pixels can more easily occur unless the focal distance of the lens is decreased. Decreasing the focal distance of the lens can, however, deteriorate resolution. In order to solve this problem, the thickness of each layer formed between the photodiode and the micro-lens may be decreased.
In addition, technology in which light is collected after changing a light path entering regions other than an optic detector may increase optical sensitivity. This light collection is performed using an image sensor including micro-lenses on a color filter. The resolution of an image sensor is largely determined by the surface characteristics of the micro-lenses. Furthermore, the surface characteristics of the micro-lenses largely depend on the material used to make the micro-lenses.
Micro-lenses can be formed by disposing an overcoat on a color filter and etching a part of the overcoat into a lens shape. Since a part of the etched surface of the overcoat works as a micro-lens, there continues to be active research directed to an overcoat material for determining the surface characteristics.
Korean Laid-open Patent No. 2008-0057118 discloses a thermosetting resin composition for a protective layer of a color filter that can have excellent adhesion strength, transparency, layer strength, heat resistance, acid resistance, alkali resistance, and storage length. However, the thermosetting resin composition can have poor stability against self-curing. Accordingly, there is a need for a new resin composition for a protective layer of a color filter.